Bolt anchor



Z. S. BEIJL BOLT ANCHOR Filed May 12, 1947 FIG.3.

n Er

Patented Oct. 10, 1950 Application May 12 ,-.1947,(Seria'1.No.'747,406 In Great- Britain February r28;:1947

41Glaims;

The invention relates to bolt anchors-such; as are used for fixingb'olts inholes drilledorother- Wise made in hard. substances. It is intended mainly, for bolts such as are used. for securing. the roofs of mines or. other underground work ings in accordance with my U. S. Patent No. 2,398,130 or for reinforcing the surrounding rock when tunnelling in accordance with my co-pending patent application No. 686,075 filed July. 25, 1946, now "Patent 2,442,113, but it :iS not limitedto these two purposes.

A well knownform ofbolt anchor comprises shield segments surroundin the bolt. and a tapered member byv whichthe segments are expanded when the bolt is screwed up; but the segments were secured together at one end, so that only the otherendexpanded and gripped the wall of the'hole. Thisform-of grip was not always satisfactory in rock formations because of the considerable clearance required tocompensate for. any relief movement of-the walls-of the hole before the insertion of the bolt. In an adap-- tation ofthis form of-bolt anchorwhich I have disclosediinthe above-mentioned patent'the segments were not secured together at the ,end; but; had to be supported bywashers and springs? against the thrust exerted by the tapered memher at the otherendQ A left handed thread was required on the bolt in that v case to ensure the expansion of the shieldsegments at both; ends of the bolt.

It is an object of theinvention'to' proyidetzan improved anchoring construction includingan' anchor which will expand evenly over its wholelength and thusprovide a.;more secure grip.

the hole in which it is placed;

It is. another objectof: theinvention to pro vide such aconstruction inJWhichthe .anchoris expanded by tapered membersfromf both ends f 4ov It is a further object of Itheinvention to pro vide a bolt with anchors atj both" ends in whi'ch' washers and springs-for supporting the anchors concurrently. s v

are notrequired'and in which"left handed screw threads are'unnecessary.

With these objects in=vieW=-the inventionis' il"- lustrated by constructional- 'forms shown 'in the accompanyin drawingsg in"which? Figure l'is'pa'rtelevation'andpart section of a bolt with two anchors according to' the inven-' tion,

but partly. broken away to show some modifica-' tions.

Throughout the description the bolt will 'be assumed-- to be insertedin the hole vertically upwards,.but this ismerely with the object of facilitating the description. In actual practice the bolt may have to be. inserted in-any direction.

Referring first to Figure 1, the apparatus comprisesan upper or firstbolt [6, a tubular 'part or member i'land a lower'or second'bolt l8 normallyv joined together by external screw threads Figure 2 "is 'an'enla'rged'sectional vlew of the upper-part of Figure *ljand H Figure 3 is --a;- view corresponding f toTigu're 71 on the bolts andfinter'nal screw threads at both ends ofthe tubular member IT. The wall thickness of the tubular member is such that ithas at leastthe' same strength "in tension as'the bolts Hi'and' IS. The loweriendof the member ll'is formed with claws at I9 like those of' a. claw v clutch, which can be engaged by a suitable tool before thebolt l8 isscrewed into, the member Figure 2 shows the anchors and related parts for the'b'olt 16in greater detail.

The bolt lfifis 'threa'ded.throughout its length,

while on"'the bolt v 18 the thread terminates short' 1 of the lower end. On each bolt a conical'nut 2f The is screwed on. to the boltapexupwards. nut Z on the. bolt Ififis screwed to abut against the upper endof the tubular member 11, while that on the bolt 1 I8 is screwed to the end of thefthread. Alternatively the nutZ may be welded or otherwise made fastto the bolt. A second nut Sof p'yr'amidaI forni is screwed on to the'top end of the bolt apex downwards. An anchor comprises four segments 4, 4 together forming a' diametrically. expansible approximately cylindrical shield or sleeve with external helical grooves 5, 5

crossing. each other or-other form of roughness to provide adequate gripping .in the hole denoted by chain dotted lines 6; 6 in Figure 2.

Each segment4 has near its lower end an in ternal' conical surface 'itapering inwardly toward theilongitudinal'center and the axis of the sleeve .to" fit the complementarily shaped outer-surface ofth'econical"nutlz 'and near its upper end a tapered or slopingflat internal surface 8'to fit one complementarily shaped outer surface or face of the pyramidal 'nut 3; Between the surfaces 1 "andnflthe'inner face of each segment 4 is cylindrial' to -iitthe bolt l when'the segments are not expanded. Lips 9,-9 at the upper end of each'segmentaproject over the end of the nut 3 to hold ,the anchorfin' place when inserting. or removin'g the boltwiththe anchor."

Both bolts are provided with anchors for holdin'g' them in'place' as will now'be describedl" A fiat circumferential groove I is provided near each end of the anchor to accommodate a ring spring II, which normally holds the segments 4, 4 together on the bolt l.

The lower bolt l8 terminates in a square head by which it may be turned.

To use the bolt for reinforcing an exposed surface underground, the bolt I6 and tubular member H are firmly screwed together, and the anchor is assembled with its nuts on the bolt IS, the nut 2 being firmly screwed against the top of the tubular member H. The conical nut 2 is preferably greased on its outer surface. The assembly is inserted in the elongated cavity or hole 6, and the assembly I6 and I1 is then'turned" in a right-handed direction by means engaging j the claws l9. from turning by friction against the sides or The segments 4, 4 are prevented.

walls of the hole 6, and the pyramidal nut 3 is held from rotating by the fiat surfaces 8, 8,

whereby thenut 3 is moved downwards. The conical nut 2 turns with the assembly l6 and I1, due to its abutting against'the end of the tubular member H or being otherwise fixed.-

The movement of the nuts 2 and 3 towards each other expands the shield segments 4, 4 because of their tapered inner surfaces land 8. Since the segments are forced outwards from both ends, the bolt I6 takes up a longitudinal position in which the outward pressure exerted by the shield is approximately balanced as between the upper and lower ends. The grip thereby exerted is substantially uniform over the whole length of the anchor. The inward pressure exerted by the ring springs I I, l l is negligible in comparison with the outward pressure due to the screwing up of I permanent installation in a tunnel or other large cavity underground, but some modifications may be required in certain cases. If it is desired to add a lining to the cavity, the lower end may be threaded as shown in Figure 3', but a portion of the bolt 18 should be left unthreaded at 2! to provide for location of the lower conical nut 2. A nut 22 holds the lining 23 in place.

Another modification is shown in Figure 3jfor the case in which it is desired to recover the reinforcement and use it again elsewhere. The upper conical nut 2 has a notch engaged by a projection 24 on the upper end of the tubular part II. The fixing of the upper part of the complete bolt assembly is effected in the same manner. as.

previously described. For removal, the lower bolt I8 is first unscrewed. It is thereby detached from the tubular member l1, and the springs l I, "H cause the segments to collapse into contact with the bolt l8, which can then be removed with the lower anchor. The tubular member I! is then unscrewed by means of the claws [9, the projection 24 ensuring the unscrewing of the conical nut 2, so that the segments 4 are released from both ends and are caused to collapse by their springs H. The bolt l6 and member H with the upper anchor can then be pulled out of the hole.

- means ofthe square end 20.

' ened up. 40

A further modification which may be suitable in certain cases is also shown in Figure 3. This relates to the outer bolt l8. The upper ends of the segments 4, 4 have conical internal surfaces 25 to engage a conical bush 26 capable of sliding on the bolt portion I8. A coil spring 2'! with washer 28 is interposed between the upper end of the bush .26 and the lower end of tubular portion I1. I The lips 9 of Figure 2 are omitted in this case.

After the upper anchor and the bolt I6 and member I! have been fixed as previously described, the bolt |8 has the anchor assembled on it with the nut 2, bush 26, spring 21 and washer 28; and the nut 2 should be at the lower end of the bolt thread. The bolt isthen screwed up by The length of the spring may be initially about 40 to 50 mm. and the free upper end of the bolt l8 about 25 mm. beyond the washer 28.

The first effect of'screwing the bolt [8 is to screw'it intothe membei l'l and to rotate the anchor with it. Whenthe bolt I8 has well entered the member, the spring 2'! bears against the lower end of the member l1. Further screwingup of the bolt l8 compresses the spring 27 until it is fully collapsed, and the shortening distance between the nut 2 and the bush 26 expands the segments 4, 4 from both ends against the walls of the hole.

The external finish of the segments need not necessarily take the form of grooves 5, but in any case the roughness of the finish will be made suitable for the kind of formation in which the bolts are to be fitted.

Where a bolt is to be permanently fixed and not recovered, it may be desirable to grout the hole with cement after the bolt has been finally tight- What I claim is:

1. Apparatus for clamping together the formation surrounding an elongated cavity comprising a first screw threaded bolt; a second screw threaded bolt; a tubular member screw threa'ded internally 'at its opposite ends and having threaded connection respectively with said bolts; a first anchor device comprising a diametrically expansible sleeve having at each end an internal surfacetapering inwardly from the adjacent sleeve end toward the longitudinal center and the axis of the sleeve, a relatively fixed nut screwed on said first bolt and abutting the adjacent end of said tubular member and having an outer sur- ,face complementary to the adjacent inwardly tapered surface of said sleeve, and an axially movable nut screwed on said first bolt and having an outer surface complementary to the other inwardly tapered surface of said sleeve; rotation .of said tubular memberand said relatively fixed nut and said first bolt together efiecting relative approaching-movement of said nuts along the sleeve aXis to thereby expand said-sleeve and cause it to grip against the walls of said cavity;

and asecond anchor device comprising a diametrically expansible secondsleeve having at each end an internalsurface tapering inwardly from the adjacentsleeve-end toward the longitudinal center and the axis of the second sleeve, a nut fast on said second bolt and having an outer surface complementary to one inwardly tapered surface of said second sleeve, and an axially movable nut screwed on said second bolt and having an outer surface complementary to the other inwardly tapered surface of said second sleeve, ro-

tation of said second bolt and the nut fast thereon effecting relative approaching movement of the nuts of said second anchor device along the second sleeve axis to thereby expand said second sleeve and cause it to grip against the walls of said cavity, and simultaneously causing said second anchor device to move bodily relatively toward said first anchor device for clamping together the formation surrounding said cavity.

2. Apparatus as set forth in claim 1 in which the sleeve of each anchor device comprises four longitudinally divided segments, and a yieldable ring spring surrounding said segments and resiliently urging them into engagement with the associated nuts.

3. Apparatus as set forth in claim 1 including axially separable means connecting the relatively fixed nut of the first anchor device with the abutting end of the tubular member for enabling said nut to be turned on said first screw by rotation of said tubular member reversely to the direction in which it is turned when efiecting relative appreaching movement of the nuts of said first anchor device. I

4. Apparatus as set forth in claim 1 including a compression spring interposed between the end of said tubular member adjacent said second anchor device and the axially movable nut of said second anchor device.

ZAKO SYTSE BEIJL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 527,406 Church Oct. 16, 1894 570,786 Church Nov. 3, 1896 719,426 Boone Feb. 3, 1903 20 1.120368 Booraem et a1 Dec. 8, 1914 

